#include<stdio.h>
int main()
{
    int grade;
    {
        scanf("%d",&grade);
        switch(grade)
        {
            case 100:
            printf("A");
            break;
            case 90:
            printf("B");
            break;
            case 80:
            printf("C");
            break;
            case 70:
            printf("D");
            default:
            printf("继续加油");
        }

    }
    return 0;
}